What is the difference?


I use FEZ Domino as MP3 player.
When it connected to my PC with usb, verything is OK. I can hear MP3 files, and I also created log file for debugging that printing to it is also OK.

When I connect FEZ Domino to 9v battery (using External Power Connector) I don’t hear anything and the log file isn’t created, so I also can’t debug it.(the lights of Domino and the MP3 board are on, so ther is power in the system)

Any idea what is happening and how to debug it?


can you flash a LED in your program, and verify that the program appears to be running?

I suspect your 9v battery is cactus and not delivering enough power for the system to run. Without a log file, that’s a sign that it’s failing to do anything - the LED test might show that nothing is going.

Then I’d try to grab a power pack (wall wart as those in the US call em) and connect that, to verify it’s not something wiring related.

using a battery might not supply enough power. It might even display 9v, but then not providing enough current.

Connecting a wall wart will probably work.

I never use any battery, because mostly they cause a lot of concerns. (empty, not completely full, etc.)

Like Brett said, you can go back to the original “LED debugging” mechanism…blink LED once on power up, then twice after initialization the file system and 3 times MP3 decoder chip…etc.

yep always best to keep a test program handy that you know works, dont mod it just keep it free for these occasions :smiley:

[quote]using a battery might not supply enough power. It might even display 9v, but then not providing enough current.

Connecting a wall wart will probably work.

I never use any battery, because mostly they cause a lot of concerns. (empty, not completely full, etc.)[/quote]

Good point. I’m currently using a 9V battery to power my Fez too; no problems yet, but it’s brand new just like my Domino. I did try to get an AC adapter from my local electronic store the other day, but I thought I’d check out a couple of details with the experts in case I fry my Domino.

What is the maximum current rating on a 9V adapter I should be looking for?

I’ve found two 9V adapters at my local electronics store; one with output current rating of 500mA and the other with 1A.


the device will only draw what it needs - so it totally depends on what you have connected to it.

In general terms, you can look at the device comparison page to see how much the device draws. The Domino is 110mA max.

If I had those two options, and they’re relatively similar pricing, I’d choose the 1A version as that means I can run much more off it than just the Domino (say an LCD and ethernet and a couple of other sensors ) and not run into challenges. The domino won’t tax the 500mA unit but the headroom you get with the other is beneficial as you want to do more.

Thanks Brett. Just want to make sure, cause I notice some electronics have a maximum input current.

You probably were right, the battery was weak.
I didn’t add new code to make the test with the leds, instead I replaced my battery and it help, but…
just for a couple of minutes and then it stopped playing again.
How can FEZ Domino can be portable if 9v battery has not enough power to play mp3 file more than1-2 minutes?
My device shouldn’t be connceted to the wall all the time.

When you connect the USB to the PC is it connected via a USB hub with external power supply?

When I connect FEZ to usb this is the way it gets the power, not from external power.
I want to use battery for power supply, not to be depend on th PC power.

It’s great that you’ve proven things work, but using a better battery.

9v batteries have notoriously bad capacity.

What type of battery were you using? Was it “fresh” just out of the packet? What was it’s shelf-life date printed on the packet? How far out was that date?

How much current does your entire system draw? What else do you have connected and how much do each of those draw?

You also need to change your program to figure out what part of your system is stopping responding, is it the MP3 player not doing it’s thing or is it the SD card (I think you’re using that?). You need to build some debugging into this - complaining isn’t helping :slight_smile:

I have no idea exactly the “typical” capacity of the 9v battery you are using. A quick Bing on the internet shows some “standard” rechargeable nimh batts being in the 200mAh range. If you’ve only used a standard alkaline you may be getting 150mAh or less.

Here’s some maths for you though. Fez Domino, on it’s own, when running requires 110mA. That means with a 200mAh rechargeable battery, at full capacity, and 100% efficiency all along the way, will run just the domino for 109 minutes. You plug in the MP3 component - more current consumed. Read the SD card - more current. What’s worse is that you’re actually burning up some of the power in heat because you’re actually feeding the 9v into a regulator that is controlling the voltage down to 5v and then 3v3, which is another loss. So you’re not doing yourself a favour in trying to use a 9v battery as a power source. Find a bigger capacity 9v battery (yes, that will most likely mean bigger size too) and you’ll be better off. Find a better way to generate the required voltage and you’re better off. Did you know a rechargeable nimh AA battery is typically 2000mAh or more? Gee, that’s a lot more capacity if you need it and it’s small too!

I don’t want to dishearten you or anything, but mobile phone manufacturers the world over spend gazillions of dollars making sure their devices are drawing the absolute minimum current possible, so they can add minutes of talk-time to their selling points, while constraining their battery capacities so the handset doesn’t get bulky or heavy. They do all this by using specialist chips and understanding the circuit inside-out and screwing down every single current consumer possible to the minimum. You at home can’t compete with that, there are compromises you will have to make. Same goes for MP3 players, the makers buy specialist parts that run at ultra low voltages so they don’t have to convert or regulate power any more than necessary. Can you make a Domino a usable, portable MP3 player? Hell yes. Can you make it last as long as your iriver clix or zune or ipod nano, sure, but at the expense of portability. Can you make a Domino match the performance of an iriver, not likely unless you were an engineer who worked on the iriver in the first place!

here’s the thing you should go buy.


along with 2x NiMH rechargeable AAs and pipe that into your 5v on the board. That will make things last much better I suspect.

SFE has it too: [url]http://www.sparkfun.com/commerce/product_info.php?products_id=8249[/url]

Thank you all for your answer and help, especially to Brett for your long and detailed answer.
I will try some of your suggetsions and see how it’s going.
I’m not familiar so much with the electricity and HW side, more with the software development, but I’ll try to work according to your answers.